This invention is in the field of sewing machines; more particularly, it is concerned with an improved basting stitch mechanism for a sewing machine needle bar and gate arrangement.
In the prior art basting stitch mechanisms exemplified in U.S. Pat. Nos. 3,559,602; 3,782,311; and 3,872,809; a latch is pivoted on a needle bar carrier which is attached to the needle bar above a needle bar driving stud, the latch having an arm extending at right angles thereto which extends between the left front surface of the driving stud so as to provide a driving connection between the driving stud and the needle bar. However, the driving stud which is connected by a connecting rod to a crank mechanism is restrained to move rectilinearly only; while the needle bar in the above cited patents swings in an arc when progressing from left needle position to right needle position or vice versa. This difference in motion between the needle bar carrier attached to the needle bar and the driving stud restrained by the crank mechanism requires a clearance between the bottom of the needle bar carrier and the top of the driving stud in order to avoid an interference. The presence of this clearance allows an impact to take place during load reversals at either extreme of the needle bar travel, resulting in noise and wear. For purposes of obtaining this clearance, the latch is carried relative to the needle bar carrier on an eccentric which must be adjusted to provide the required clearance.
Also, it would be ideal in any needle bar to provide for release of the needle bar from the endwise reciprocation imparting mechanism in the event of a loading on the sewing needle approaching its breaking strength.
What is required is an improved basting stitch mechanism in which there is no necessity to set clearance to avoid noise and wear due to the impact between the needle bar carrier and the driving stud. Further, such an improved basting stitch mechanism should provide for release of the needle bar on encountering a loading which could cause needle breakage.